Many who have had the natural lens of the eye damaged as by injury or by disease require surgery resulting in removal of the natural lens. This condition of lens removal is known as aphakia and must be corrected by the use of a high plus corrective lens in order to restore vision.
Such corrective lenses may be in the form of spectacles or contact lenses, but contact lenses are preferred since spectacles are not only cosmetically undesirable because of their thickness to provide the correct vision, but in addition produce an excessively large image on the retina. Even with the most suitable lenses, including contact lenses, presently in use, vision is not as desirable as it should be for the aphakic individual since such lenses do not adequately compensate for certain changes in light transmission which occur in the absence of the natural human crystalline lens. The result is a lack of visual acuity and high chromatic aberration in aphakic individuals.
A considerable portion of incident light entering the eye is absorbed by various parts of the eye, as described herein, so that only the unabsorbed or transmitted portion strikes the retina. The incident light is, of course, comprised of the entire spectrum of wavelengths including the ultraviolet, visible and infrared.
Specifically, the cornea preferentially absorbs that portion of the light with wavelengths up to about 340 mmu. The crystalline lens preferentially absorbs the wavelengths from about 340 up to about 400 mmu. There is also a characteristic absorption of the visible portion of the spectrum by various parts of the eye. The overall result of the various absorptions in the human eye is to permit the unabsorbed light to be transmitted to the retina, this light being defined by wavelength and intensity at each wavelength. It is apparent that in the aphakic eye, where there is no crystalline lens, light from 340 to 400 mmu will be transmitted to the retina and that absorption in the visible range of the spectrum will also be changed to the extent that such visible light was absorbed by the crystalline lens. In other words, the spectrum of the light striking the retina in the aphakic eye is different from that in the normal eye.